Artificially lifting fluid from deep wellbores requires a very carefully designed system, or otherwise the cost of production can exceed the value of the produced fluid. Extremely deep wells require that the borehole be of very small diameter, thereby necessitating the use of a pumping means of a small diameter, so that the pump can be accommodated by the slim hole.
Downhole hydraulically actuated pumps eliminate the necessity for pumpjacks, sucker rod strings, and electrical wires, all of which contribute to reduction in production costs. It is desirable to provide a downhole pump with as large a diameter engine piston and pump piston as possible so that each stroke of the pump apparatus produces a maximum quantity of fluid. All hydraulically actuated downhole pumps must have a housing which forms a working chamber for the engine piston and the production piston, and the interior of the housing represents the maximum diameter any downhole pump can enjoy. In the past, most downhole pumps require fluid passageways leading to and from various expansion chambers of the pump, and this expedient greatly reduces the size of the engine and pump pistons. The present invention provides improvements in downhole pumps having a maximum diameter engine piston and pump piston.
In one form of the present invention, there is provided apparatus and method by which the bottom of the wellbore can be chemically treated by utilizing spent power fluid that previously was admixed with treatment chemical.
In another form of the invention, formation fluid flows into the lower end of the pump, up through a hollow connecting rod extension, into the production piston, and through a pair of intake valves located within the production piston, thereby providing the production end of the pump with a formation fluid inlet and a set of intake valves all located within the reciprocating production piston.